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weaknesses in the Goat Trail are presently observed. The geological structure of the <br />• slope which the Goat Trail is constructed consists primarily of massive sandstone with <br />some intermixed beds of shale and cool. These beds dip away from The slope face at <br />approximately 4° and are the only through-going discontinuities observed. Due to <br />the dip of The beds within the slope, a rock mass would Tend to slide into rather than <br />away from the slope face increasing the stability of the slope. For a massive failure <br />to occur, a failure surface which would cut across the bedding planes must first be <br />defined. A "worst case" example of the slope on which the Goaf Trait is constructed <br />has been selected for a stability analysis. This slope has an angle of 85° and is <br />80.4 feet in height, as shown on Table 3.5-7. A conservative value of 37° was used <br />as a friction angle, which is the angle of repose for the material when it is broken. <br />The location of this cross section is shown on Exhibit 3.5-I. The theories, procedure <br />and assumptions used to calculate the factor of safety were taken from Rock Slope <br />Engineering, Chapter 7, "Plane Failure," Revised Third Edition, written by E. Hoek and <br />J. W. Bray. <br />3.5.7.2 Procedure for Calculating Factor of Safety <br />• The first assumption that must be made concerns the shape of the failure. In <br />steep rock slopes where no planes of weakness are observed, the failure surface would <br />follow minor geological features and would be almost planar. In order that sliding <br />occurs on a single plane, the following geometrical conditions rnusT be satisfied: <br />I. The plane on which sliding occurs must strike parallel or nearly parallel <br />(within approximately ± 20°) to the slope face. <br />2. The failure plane must "daylight" in the slope face. This means that its dip <br />must be smaller Than the dip of The slope face, yr yf > gyp <br />3. The dip of the failure plane must be greater than the angle of friction of <br />this plane, or yp > Q <br />4. Release surfaces which provide negligible resistance to sliding must be <br />present in the r ck mass to define the lateral boundaries of the s'~de. <br />The slope which the Goat Trail is constructed is considered to be a dry slope. <br />Although there may be moisture present, There is no pressure generated within the <br />• slope which would influence its stability. For dry slopes The critical failure can be <br />calculated using the following equation: <br />3.5-8 <br />.+ _.i aim <br />